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At least 1,279 records · Page 71Linked to original sources
PubMed2003

Organometallic sesquialkoxides of aluminium, gallium and indium.

Organometallic sesquihalides of aluminium are important intermediates in technical processes. However, those compounds and their homologues with gallium or indium centers have not been structurally characterized so far. On the other hand organometallic sesquialkoxides have been isolated. The major synthetic routes and the structures of the corresponding products will be discussed. Furthermore, cage-contructiveness reactions having sesquialkoxides as educts will be shown. Discussion will focus primarily on the syntheses, the spectroscopic findings and a structural comparison. Especially the structural motifs deserve attention because of the structural connection to the well-known earth metal alkoxides.

Journal Article↗
PubMed2003

Template assisted design of microporous gallium nitride materials.

For the first time the synthesis of a porous gallium nitride material (GaN1.15H1.18O0.06C0.04) with narrow pore size distribution in the micropore regime using a nonylamine assisted sol-gel route is reported. The yellow solid has a very high micropore volume of 0.176 cm3 g(-1) comparable to that of zeolitic solids.

Journal Article↗
PubMed2004

Dichloro and alkylchloro gallium derivatives of dichalcogenoimidodiphosphinate ligands: isolation of a spirogallium cation.

Dichloro and chloromethyl Ga(III) complexes of general formulae [XClGa-eta2-{R2P(E)NP(E'R'2-E,E'}](X = Cl, R, R'= Ph, E, E'= O (1), S (2), Se (3); R = Ph, R'= OEt, E = O, E'= S (4); R = Me, R'= Ph, E, E'= S (5) and X = Me, E, E'= O (6), S (7), Se (8)) were synthesised by either metathesis reactions between GaCl3 and the potassium salt of the ligand (X = Cl) or by methane eliminations from in situ prepared GaMe2Cl and the protonated ligands LH (X = Me). Redistribution reaction of (3) in either CDCl3 or THF afforded the solvent-free tetracoordinate gallium spirocycle cation [Ga-{eta2-{Ph2P(Se)NP(Se)Ph2-Se,Se'})2]+ (9+). The molecular structures of complexes 2, 4, 5, 7 and 9(+) show non-planar gallacycle rings.

Journal Article↗
PubMed2006

Hydrido and chloro gallium and aluminium complexes with the tridentate bis(2-dimethylaminoethyl)amide ligand.

Five-coordinate gallium and aluminium dihydrides, H2Ga[N(CH2CH2NMe2)2] () and H2Al[N(CH2CH2NMe2)2] (), were synthesized and found to be volatile and thermally stable. and reacted with H3Ga(NMe3) and H3Al(NMe3), respectively, to form H2Ga[N(CH2CH2NMe2)2]GaH3 () and H2Al[N(CH2CH2NMe2)2]AlH3 (), in which the amido nitrogen bridged between the MH2 and MH3 groups (M=Ga or Al). A mixed metal complex, H2Al[N(CH2CH2NMe2)2]GaH3 () was obtained from the reaction of with H3Al(NMe3) or with H3Ga(NMe3), and a crystal consisting of a mixture of and was structurally characterized. The five-coordinate chloro derivative, Cl2Ga[N(CH2CH2NMe2)2] (), was synthesized and characterized.

Journal Article↗
PubMed1999

Hair removal using an 810 nm gallium aluminum arsenide semiconductor diode laser: A preliminary study.

BACKGROUND: Laser hair removal is a popular treatment method for removing unwanted hair. Several laser systems are available for laser hair removal. The gallium aluminum arsenide semiconductor diode (GAASD) laser is one of the newer laser modalities to be studied. OBJECTIVE: To evaluate the efficacy of the GAASD laser system in removing unwanted hair. METHODS: Twenty-six patients with brown or black hair growth were treated with the GAASD laser at fluences of 20-80 J/cm2. Hair regrowth was measured 4 weeks after the first treatment, 4 weeks after the second treatment, 4 weeks after the third treatment, and 4 weeks, 8 weeks, and 8 months after the fourth treatment. CONCLUSION: GAASD laser treatment resulted in hair growth delay in all treated regions. Repeated laser treatments did not produce an increased number of vellus hairs. The percentage of hair reduction fluctuated between 5% and 13% with the second or third treatment averaging the highest percent reduction. In all cases, the percentage of hair reduction of the treatment sites evaluated at 8 months after the fourth treatment was less than both the second and third treatments (highest average percent reduction) and the fourth (last) treatment.

Adult↗
PubMed2006

Hydrostatic-pressure-induced porous gallium nitride from nanotube bundles: an ab initio study.

Ab initio calculations show that (5,5) and (6,6) single-walled gallium nitride nanotubes (GaN NTs) in bundles could aggregate spontaneously to form new condensed phases when bundled tubes are close enough under hydrostatic pressure. The new GaN phases have typical porous structures, constructed by alternating tetragons and hexagons around the original tube walls. Owing to the different compatibilities of the chirality of the tube with the symmetry of the array, the new phase formed from (5,5) GaN NT bundles is triclinic and that from (6,6) ones is hexagonal. These porous GaN phases possess tetrahedral bonding corresponding to sp(3) hybridization, different from sp(2) hybridized bonding in individual GaN NTs. The interaction between tubes not only controls the structural transformation but also influences the electronic structure of porous GaN. We expect that the two-dimensional-channeled porous structure of GaN is advantageous for the usage of GaN as the molecular sieve and as the excellent dilute magnetic semiconductor by considerable magnetic doping.

Journal Article↗
PubMed1970

Solar abundance of gallium.

The spectral region around the lambda4172 A resonance line of gallium has been synthesized at disk positions mu = 1.0, 0.5, and 0.3. The center-limb variation can be reproduced by Elste's semiempirical model if a macroturbulent smearing of the emergent spectrum due to mass motions with mean velocity decreasing with altitude are introduced. The abundance of Ga derived from disk position mu = 1 is found to be log [N(Ga)/N(H)] + 12 = 2.80.

Journal Article↗
PubMed1990

Interest of gallium hepatic scintigraphy in hepatic abscess: a case study.

The interest of 67Ga-citrate scintigraphy in the diagnosis of hepatic abscess is illustrated by a study of a 56-year-old man, who was admitted to the hospital for upper abdominal pain. Ultrasound (US) and X-ray CT scan examinations suggested the presence of a liquid mass, the origin of which was unclear. Liver scintigraphy with 67Ga-citrate disclosed a lacunar zone surrounded by a rim of increased uptake, an image strongly suggestive of abscess or necrotic tumor. A US-guided needle aspiration of the hepatic mass yielded a purulent liquid, from which Streptococcus milleri were grown. This observation suggests that, despite the development of other diagnostic procedures, hepatic gallium scintigraphy still remains sometimes useful for the investigation of poorly characterized hepatic masses.

Citrates↗
PubMed1995

Developmental competence of mouse embryos following zona drilling using a non-contact holmium:yttrium scandian gallium garnet (Ho:YSGG) laser system.

The purpose of this study was to assess the efficacy of the holmium:yttrium scandian gallium garnet (Ho:YSGG) laser, operating in a pipette-free, non-contact mode, to assist hatching and sustain normal embryonic development. Two-cell mouse embryos were recovered and assigned to laser-assisted hatching (LAH) treatment or control human tubal fluid (HTF) culture with or without serum (HTF-s, HTF-o) or with late serum supplementation (HTF-o/s). The basic experimental apparatus for LAH consisted of a stationary 2.1 microns Ho:YSGG laser beam directed through a mechanical shutter into an input port of a Zeiss Axiomat inverted microscope. Fewer (P < 0.05) embryos developed to the blastocyst stage in the HTF-s group (81%) than in the LAH (90%), HTF-o (94%) and HTF-o/s (92%) groups. The level of hatching was significantly increased (P < 0.01) after the LAH treatment (57%) compared to HTF-o/s (32%), HTF-s (18%) or HTF-o (5%). Implantation rates were not significantly impaired following the LAH treatment (21%). These data demonstrate that LAH using the Ho:YSGG laser is a simple, accurate and effective procedure for assisted hatching.

Animals↗
PubMed2006

Induction, helicity, and alpha effect in a toroidal screw flow of liquid gallium.

We investigate experimentally induction mechanisms in a screw flow of gallium in a toroidal channel. The flow is nonstationary and operated in a spin-down regime: the channel (and fluid) are initially set into solid body rotation; as the channel is stopped the fluid is set into strong helical motion by diverters located inside the channel. In this study, we put a particular emphasis on the induction generated by these helical motions, which are expected to develop over the entire range of turbulent scales. We apply an external magnetic field either perpendicular to the channel axis parallel to it. At large scales the nonlinear induction mechanisms are associated with the Parker stretch and twist effect and with the expulsion due to overall rotation. Induction mechanisms can also originate in the small scale helicity as in the alpha induction effect of mean-field magnetohydrodynamics. Our measurements yield an upper bound for the alpha coefficient, significantly lower than estimates based on dimensional analysis. We discuss the consequences of our observations for the engineering of homogeneous dynamos in the laboratory.

Journal Article↗
PubMed2001

Grain Boundaries in Gallium Arsenide Nanocrystals Under Pressure: A Parallel Molecular-Dynamics Study.

Structural transformation in gallium arsenide nanocrystals under pressure is studied using molecular-dynamics simulations on parallel computers. It is found that the transformation from fourfold to sixfold coordination is nucleated on the nanocrystal surface and proceeds inwards with increasing pressure. Inequivalent nucleation of the high-pressure phase at different sites leads to inhomogeneous deformation of the nanocrystal. This results in the transformed nanocrystal having grains of different orientations separated by grain boundaries. A new method based on microscopic transition paths is introduced to uniquely characterize grains and deformations.

Journal Article↗
PubMed2002

High-frequency acoustic modes in liquid gallium at the melting point.

The microscopic dynamics in liquid gallium at melting has been studied by inelastic x-ray scattering. We demonstrate the existence of acousticlike modes up to wave vectors above one-half of the first maximum of the static structure factor, at variance with earlier results from inelastic neutron scattering [F. J. Bermejo et al., Phys. Rev. E 49, 3133 (1994)]. Despite structural (extremely rich polymorphism) and electronic (mixed valence) peculiarities, the collective dynamics is strikingly similar to the one of van der Waals and metallic fluids. This result speaks in favor of the universality of the short time dynamics in monatomic liquids rather than of system-specific dynamics.

Journal Article↗
PubMed2004

Why do gallium clusters have a higher melting point than the bulk?

Density functional molecular dynamical simulations have been performed on Ga17 and Ga13 clusters to understand the recently observed higher-than-bulk melting temperatures in small gallium clusters [Phys. Rev. Lett. 91, 215508 (2003)]]. The specific-heat curve, calculated with the multiple-histogram technique, shows the melting temperature to be well above the bulk melting point of 303 K, viz., around 650 and 1400 K for Ga17 and Ga13, respectively. The higher-than-bulk melting temperatures are attributed mainly to the covalent bonding in these clusters, in contrast with the covalent-metallic bonding in the bulk.

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PubMed2004

Phase coexistence in gallium nanoparticles controlled by electron excitation.

In gallium nanoparticles 100 nm in diameter grown on the tip of an optical fiber from an atomic beam we observed equilibrium coexistence of gamma, beta, and liquid structural phases that can be controlled by e-beam excitation in a highly reversible and reproducible fashion. With 2 keV electrons only 1 pJ of excitation energy per nanoparticle is needed to exercise control, with the equilibrium phase achieved in less than a few tenths of a microsecond. The transformations between coexisting phases are accompanied by a continuous change in the nanoparticle film's reflectivity.

Journal Article↗
PubMed2004

Unusual freezing and melting of gallium encapsulated in carbon nanotubes.

The freezing and melting behavior of gallium (Ga) encapsulated in carbon nanotubes was investigated through in situ observation in a transmission electron microscope. It is shown that Ga remains liquid up to -80 degrees C when encapsulated in carbon nanotubes. Results of detailed electron diffraction analysis show that the encapsulated Ga can crystallize in either beta phase or gamma phase rather than the common alpha phase upon freezing. Both beta-Ga and gamma-Ga melt at around -20 degrees C. While this is very close to the melting point of bulk beta-Ga (-16 degrees C), it is considerably higher than that of bulk gamma-Ga (-35.6 degrees C). It was observed that upon solidification, Ga has its unique crystallographic orientation relative to the host carbon nanotube.

Journal Article↗